A Cute Appendix: Equivocal Imaging Findings in the Diagnosis of Acute Appendicitis

By Elana Liebow-Feeser

CASE

Summary: A 48-year-old female with a history of hypertension, three C-sections, and no substance use presented to the ED with one day of generalized abdominal pain. She awoke in the middle of the night by sharp, constant 9/10 generalized abdominal pain and subjective abdominal distension. She denied chest pain, SOB, back pain, nausea, vomiting, headache, blurry vision, fever, chills, cough, lower extremity pain or edema. She was able to pass flatulence and had a bowel movement later that morning. She denied constipation, diarrhea, hematochezia or melanotic stool. She denied dysuria, although noted that an outpatient UA performed that morning was positive for RBCs. She still menstruated regularly and was not concerned about pregnancy or STIs. Of note, her abdominal pain remained constant and gradually localized to the RLQ over the course of the day prior to and while in the ED.

Vital Signs: BP: 196/121 HR: 89 RR: 20 SpO2: 99% T: 36.7C

Pertinent Physical Exam: Abdomen is soft and slightly distended. Normoactive bowel sounds auscultated bilaterally. Generalized abdominal pain with increased severity in RUQ and RLQ compared to left. (+) rebound tenderness. (+) Rovsing’s sign. No guarding. No CVA tenderness. On pelvic exam, no CMT or adnexal tenderness. Moderate amount of whitish-yellow thin discharge pooling in speculum. STI and yeast cervical swabs collected. On follow-up exam, abdominal pain worsened in RLQ.

Pertinent Lab Results: CBC: WBC 14.48, Hgb 14.4, PLT 320K / HCG pregnancy negative / Serial troponins negative / Lactate 1.6 / Lipase 29 / CMP normal / UA in ED normal / STI panel (CT, GC, Trich) negative

Pertinent Imaging Results: CT abdomen/pelvis with IV Contrast: (1) The appendix is fluid-filled measuring up to 0.6 cm, no peri-appendiceal fat stranding and without any other secondary signs to suggest acute appendicitis. (2) No hydronephrosis or obstructing renal stones.

Diagnosis and Management: Given the patient’s equivocal imaging findings but physical exam and history concerning for acute appendicitis, general surgery service was consulted for further evaluation and management. The patient was admitted to the general surgery service for serial abdominal exams and was eventually discharged after improvement of her symptoms.

Clinical Question: What is the best course of management and disposition for patients with equivocal imaging findings but history and physical exam concerning for acute appendicitis in the emergency department?

SUMMARY OF EVIDENCE

With a lifetime incidence of 6.7% in females and 8.6% in males in the United States, acute appendicitis (AA) represents a significant portion of acute abdominal pathologies. [1] Complications of AA can be serious, with those such as perforation occurring in 17% to 32% of patients. [2] The medical community, particularly emergency medicine physicians and general surgeons, are faced with the challenge of balancing the goals of early identification of AA with avoidance of non-therapeutic surgery.

Historically, the diagnosis of AA in the ED setting has incorporated a combination of (a) classic signs and symptoms, such as epigastric abdominal pain migrating to the right lower quadrant and positive Rovsing sign, (b) imaging, principally CT with IV contrast and ultrasound, depending on the patient population, and (c) clinical decision rules, such as the Alvarado Score (Table 1). [3] However, lack of consensus on the nuances of how and when to use tools such as imaging and decision rules persists among different societies’ guidelines, such as the American College of Emergency Physicians and the World Society of Emergency Surgery. [4,5] Regarding treatment, the 2024 Society of American Gastrointestinal and Endoscopic Surgeons (SAGES) Guidelines conditionally recommend operative over non-operative management of AA and state that in cases of uncomplicated AA surgical treatment may be performed immediately (<12 hours) or delayed (>12 hours), although note that evidence is weak for the latter recommendation. [6] However, surgery should not be avoided altogether, as a 2022 meta-analysis of RCTs found non-operative treatment with antibiotics has reduced efficacy compared to appendectomy in adults ≥16 years (RR 0.75, 95% CI 0.63 to 0.89). [7]

Given the above context, it is important to understand the incidence of acute appendicitis among patients with equivocal CT findings. In one retrospective study of 1,344 adult patients who underwent CT with IV contrast for work-up of suspected acute appendicitis at the University of Michigan Medical Center, 172 (13%) had indeterminate imaging findings. [8] Of these indeterminate cases, nearly a third (31%) were subsequently diagnosed with AA. [8] The authors further analyzed equivocal CT results by sub-categories of findings, and found that, while <6 mm is a largely agreed upon upper threshold for normal appendiceal diameter, patients with appendiceal diameters <9 mm and no other abnormal findings had a lower likelihood of AA. [8] Conclusions that can be made from the sub-divided results in this study are limited given the relatively lower numbers of patients included in each group combined with some variability in CT reader #1’s and #2’s reads. However, more recent studies’ findings have also called the 6mm appendiceal diameter threshold into question. [9]

In a 2023 retrospective study of 103 patients aged ≥15 years with equivocal CT findings for AA, 31 (30%) went on to be diagnosed with AA. [10] Of note, all of these cases of appendicitis were uncomplicated. This study aimed to identify clinical features and CT findings predictive of AA in patients with equivocal CT results. The authors found that Alvarado score ≥7 and appendiceal wall thickness ≥2 mm were independent predictors of AA with respective adjusted OR of 1.47 (95% CI 1.12 to 1.94) and 2.76 (95% CI 1.09 to 7.02). [10] However, interpretation of the below recommendations should consider the limitations of generalizability with this being a single-center study based in Thailand.

Table 1. Alvarado Score for Acute Appendicitis adapted from MDCalc [11,12]

Predicts likelihood of acute appendicitis diagnosis in patients with suspected acute appendicitis.
Signs
Right lower quadrant tenderness	+2
Elevated temperature (37.3°C or 99.1°F)	+1
Rebound tenderness	+1
Symptoms
Migration of pain to right lower quadrant	+1
Anorexia	+1
Nausea or vomiting	+1
Laboratory Values
Leukocytosis >10,000	+2
Leukocyte left shift (>75% neutrophils)	+1
0-4: unlikely appendicitis 5-6: possible appendicitis 7-8: probably/likely appendicitis ≥9 (males), ≥10 (females): definite appendicitis à consider treatment of presumptive appendicitis without CT imaging

RECOMMENDATIONS

Given high incidence of AA despite equivocal CT findings, such equivocal CT findings should not be used to definitively rule out the diagnosis of AA nor prompt subsequent discharge without further work-up or monitoring.
When you have high clinical suspicion for AA but equivocal CT findings, consult general surgery early so they may monitor clinical status with serial abdominal exams.
While the data remains limited based on available studies, in cases of low-risk clinical features and equivocal CT findings, but appendiceal wall thickness <2 mm, it is reasonable to observe patients for up to 12 hours post-symptom onset and track their clinical progression with serial abdominal exams in the ED. However, this decision should be made on a case-by-case basis, incorporating clinician experience, availability of general surgery, and other setting-dependent factors.

REFERENCES

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